The Bacteria in Your Gut Are Deciding How Much You Weigh

In 2004, a remarkable experiment changed everything we thought we knew about weight. Professor Fredrik Backhed took skinny mice that had been raised with no gut bacteria at all and introduced bacteria from the guts of obese mice. Within weeks, without changing their diet, the previously lean mice became obese, gaining 60 per cent more weight. Even when the researchers reduced their food, the mice kept gaining.

A human study confirmed it. Bacteria from an obese twin made mice obese. Bacteria from the lean twin kept mice lean. Same food. Different microbiome. Different outcome.

The difference comes down to two families of bacteria. Firmicutes are experts at extracting every possible calorie from your food. The more you have, the more energy your body absorbs.

Bacteroidetes do the opposite, extracting essential nutrients and allowing excess calories to pass through, carried out in your stool on the back of dietary fibre.

What feeds Bacteroidetes? Fibre. What starves them and lets Firmicutes take over? A diet stripped of fibre, loaded with sugar and refined carbohydrates. The modern Western diet.

If you have struggled with your weight and felt it could not simply be explained by how much you eat, you may be right. The composition of your microbiome, shaped by what you eat, may be doing as much to determine your body weight as the calories on your plate.

Your action today: Feed your good bacteria. Add a handful of mixed vegetables or a side salad to your next meal. The more variety of fibre you eat, the more diverse your microbiome becomes.